Giving up all desires born of the will, withdrawing the
senses from every direction by strength of mind, attain tranquility little by
little with the help of the budhi armed with fortitude. Once the mind is
established in the Atman, one should not think of anything else. Whenever the
fickle and unquiet mind strays, withdraw it and restore it to the control of
the Atman alone. (Bhagavad Gita 6 - 24 – 26)

If the intellect, being related to a distracted mind, loses its discrimination and therefore always remains impure, then the embodied soul never attains the goal, but enters into the rounds of births. (Katha Upanishad, 1.3.7)

If the intellect, being related to a mind that is restrained, posseses discrimination and therefore always remains pure, then the embodied soul attains that goal from which one is not born again. (Katha Upanishad, 1.3.8)

Charity, discharge of one’s duties, tranquillity of the mind and the senses, study of scriptures, various kinds of rituals and vows — all these have control of the mind as their one object. Subjugation of the mind is samadhi. It is the highest yoga. (Bhagavad Purana, 11.23.46)

Doubtless, O mighty-armed, the mind is intractable and restless; but by practice and detachment, O son of Kunti, it can be controlled. (Bhagavad Gita, 6.35)